The present invention relates generally to image generating systems, and more particularly to optics arrangements and light source arrangements especially suitable for miniaturized image generating systems such as the miniaturized image generator disclosed in copending U.S. patent application Ser. No. 08/362,234, now U.S. Pat. No. 5,808,800, entitled ACTIVE MATRIX LIQUID CRYSTAL IMAGE GENERATOR and copending U.S. patent application Ser. No. 08/361,775 entitled DC FIELD-BALANCING TECHNIQUE FOR AN ACTIVE MATRIX LIQUID CRYSTAL IMAGE GENERATOR filed cotemperaneously herewith, which applications are incorporated herein by reference.
One of the ongoing challenges facing the manufacture of miniature image generating systems is providing smaller and smaller systems. Miniature image generating systems which are small enough to be mounted onto a helmet or small enough to be supported by a pair of eyeglasses will find a wide variety of uses if they can provide adequate resolution and brightness in a small, low-power package at a low cost. Conventional technologies such as CRTs are difficult to miniaturize and therefore do not hold much promise in this field. Alternatively, new systems based on VLSI integrated circuits are currently being developed which provide much smaller spatial light modulators for use in a miniaturized image generating systems. However, one of the problems in this field is providing optics and illuminating arrangements which may be scaled down in coordination with the miniaturized spatial light modulator in order to provide an overall image generating system which is practical and compact enough to be mounted onto a helmet or supported by a pair of glasses. Another problem in this field is providing an illuminating arrangement which requires as little power as possible in order to make the overall system more portable.
Referring to FIG. 1, a prior art miniature image generator system generally designated by reference numeral 10 will be described. System 10 includes a transmissive spatial light modulator 12 which modulates light from a light source 14 positioned immediately adjacent to spatial light modulator 12 by selectively changing the polarization of light passing through the spatial light modulator. A polarizer 16 is positioned between light source 14 and spatial light modulator 12 which allows light of one polarization from light source 14 to enter spatial light modulator 12. An analyzer 18 is positioned adjacent to the opposite side of spatial light 12 which allows light of a particular polarization to pass through analyzer 18. An eyepiece lens 20 having a focal length F1 is positioned approximately one focal length F1 from spatial light modulator 12 such that a viewer may see a virtual image of the pattern of modulated light formed by spatial light modulator 12 when the viewer""s eye is positioned in an appropriate location. As shown in FIG. 1, this arrangement results in a viewing region indicated by reference numeral 22 from which a viewer may view the entire virtual image of the pattern at modulated light produced by the spatial light modulator display.
In the above described arrangement, since light source 14 is positioned adjacent to spatial light modulator 12, light source 14 must have a light emitting surface with essentially the same surface area as spatial light modulator 12. Also, in order for the optics to perform properly, the light source is a diffuse light source. However, these requirements causes two major problems. First, a large diffuse light source as described above is substantially more expensive than other types of light sources. Second, because light source 14 is diffuse, a large percentage of the light generated by light source 14, indicated by lines 24, is directed to areas which are not within viewing region 22 including areas in which the light does not pass through eyepiece lens 20. This wastes a large percentage of the light produced by light source 14 and requires much more light to be produced than would be necessary if substantially all of the available light were directed into viewing region 22. This wastage of light significantly increases the power requirements of the overall system. As will be seen hereinafter, the present invention provides a variety of novel optics arrangements including novel light source arrangements which, when combined with miniaturized spatial light modulators, are capable of providing low power, compact miniaturized image generating systems that may be used to produce a direct view miniature display.
As will be described in more detail hereinafter, a system for producing modulated light is disclosed. The system comprises a spatial light modulator including a light modulating medium switchable between different states so as to act on light in ways which form overall patterns of modulated light. The system also includes means for switching the modulating medium between the different states in a controlled way and illumination means for producing a source of light. The system further includes optics means for directing light from the source of light into the spatial light modulator and for directing light from the spatial light modulator through a predetermined source imaging area. The optics means cooperates with the illumination means and the spatial light modulator so as to produce a real image of the source of light within the source imaging area such that an individual is able to view a virtual image of the overall patterns of modulated light from the source imaging area.
In one preferred embodiment of the present invention the spatial light modulator is a reflective type spatial light modulator and the optics means cooperate with said illumination means and said spatial light modulator such that some of the light passing from the illumination means to the spatial light modulator overlaps with some of the light passing from the spatial light modulator to the source imaging area.
In another embodiment of the present invention, the light source is provided by means of an array of light emitting sources such as LEDs (light emitting diodes) spaced apart by a predetermined distance. These spaced apart light sources, in combination with the optical components, produce an equal plurality of images at the source imaging area which are spaced apart from one another by a predetermined distance. The optical components of this embodiment may include a single collimating lens disposed optically between the light sources and the spatial light modulator, or alternatively, may include a plurality of collimating lenses, each of which is disposed optically between an associated one of the light sources and the spatial light modulator so as to direct light from its associated light source to a corresponding portion of the spatial light modulator.
In the case of a plurality of collimating lenses, the optical components also include a single eyepiece lens which is disposed optically between the spatial light modulator and the source imaging area and which defines a much greater focal length than the focal length of each of the individual collimating lenses. Also, the light sources may be disposed optically approximately a focal length away from their associated collimating lens, such that the plurality of images produced at the source imaging area a substantially larger than their respective light sources. Alternatively, in this arrangement, the light sources are disposed optically slightly closer to their associated collimating lens than one focal length so as to cause each collimating lens to direct light from its associated light source to the spatial light modulator in a slightly diverging manner. The spatial relationship between the light sources and the divergence of the light from the collimating lenses are such that the plurality of images produced at the source imaging area overlap one another in a predetermined way.
The plurality of light sources may be provided in a variety of arrangements. In a first arrangement, the arrangement includes a single dielectric substrate having on one surface a pattern of electrically conductive leads adapted for connection to a source of electric power. A plurality of LEDs are individually attached to the substrate and electrically connected with the pattern of leads. An equal plurality of individual collimating lenses are attached to the substrate and disposed optically over associated ones of the LEDs. In a second arrangement, the arrangement includes a single LED wafer having on one surface a pattern of electrically conductive leads adapted for connection to a source of electric power. The pattern of leads divides the wafer into the plurality of LEDs. An equal plurality of individual collimating lenses may be attached to the wafer and disposed optically over associated ones of the LEDs. Alternatively, the arrangement includes a single substrate which is attached to the LED wafer and which is integrally formed to define an associated collimating lens for each of the LEDs. In a third arrangement which may be any combination of the first and second arrangement, the plurality of LEDs include LEDs of different colors thereby providing a color version of the miniaturized assembly.
In a color version of the present invention, the light sources include different color light sources, such as LEDs, which are spaced apart a predetermined distance d and which emit light outwardly at a maximum angle A. A light diffusing plate is spaced from the light sources a distance L. Thus, the positional relationship between the light sources and the diffusing plate is such that L is at least approximately equal to d/A. In this way, as will be seen, it is possible to obtain proper registration of the different color images even though the light sources are spaced apart from one another.
As will be described in more detail hereinafter, a variety of specific arrangements for the optical components of the system for producing modulated light are also disclosed. These arrangements include specific combinations of a variety of light sources, polarizers, beam splitters, analyzers, lenses, mirrors, and holographic optical elements arranged to direct the light from the light source into the spatial light modulator and from the spatial light modulator to the source imaging area.